An interactive hierarchical tree visualization displays world population data organized by continent, country, and city, with color-coded nodes indicating each level. Hovering over city nodes reveals population details through a tooltip. The visualization uses D3.js version 7 with the `d3.hierarchy` and `d3.tree` layouts, `d3.linkVertical` for edges, and SVG rendering. It loads data from a CSV URL via `d3.csv` with fallback to embedded sample data, and includes validation and error handling.